Power converters are used to convert electrical power having one voltage level (e.g., 12V) to electrical power having a different voltage level (e.g., 3V). Power converters can also be used to convert power having one type (e.g., alternating current (AC) power) to power having a different type (e.g., direct current (DC) power). Switching mode power converters are widely used because of their high efficiency. Generally, switching mode converters are either inductor and transformer based or capacitor based without a magnetic component.
In the case of a transformer-based architecture, the power converter includes two coils that are inductively coupled to each other, such as two coils sharing a common core formed of magnetic material. A primary coil is coupled to the input circuitry of the transformer, a secondary coil is coupled to the output circuitry of the transformer, and power conversion is provided according to a ratio of turns of the primary and secondary coils. In the case of a capacitor-based converter architecture, the power converter includes multiple switches (e.g., transistors such as field-effect transistors (FETs)) that operate under the control of a controller to selectively charge capacitors in series or in parallel, to provide a desired output power level.
Transformer-based converters are typically used for applications where isolation is required between input and output voltage rails, or application with a big voltage conversion ratio. However, transformer-based converters require large sized magnetic components due to their higher AC losses and limited switching frequency. A need therefore exists for a transformer architecture that can run at higher switching frequency and provide reduced magnetic component sizes.
Moreover, conventional transformer-based converters include forward, flyback, push-pull, half-bridge, and full-bridge PWM converters and various resonant converters. A typical example converts a 48 V input voltage to a 12 V output. For such a converter, because of the higher voltage stress on the input side, power MOSFETs (metal-oxide-semiconductor field effect transistors) on the transformer primary side are high-voltage rated MOSFETs that suffer not only from high switching losses but also have high conduction losses due to a high on-resistance Rds(on). As a result, the maximum switching frequency of the converter is limited due to the higher power dissipation and power device thermal stress. Because of the limited switching frequency, the conventional transformer-based solutions usually need a large size power transformer and large size output inductor and thus provide low converter power density. A need therefore exists for a transformer architecture that can provide reduced high power density while being configured to handle elevated voltage levels.